Method and apparatus for reproducing optical information

ABSTRACT

The disclosure relates to a method and apparatus for storing and reproducing information using a deformable material containing a volumetrically homogeneous distribution of particles for scattering light transmitted through said material. The information can be introduced and read-out in optical form.

United States Patent Chafaris I [54] METHOD AND APPARATUS FOR REPRODUCING OPTICAL ENFORMATION [72] Inventor: George J. Chafaris, East Syracuse, NY. [73] Assignee: General Electric Company [22] Filed: June 22, 1959 [21] Appl. No; 822,097

[52] U.S.Cl ..96/l.l,96/1.5, 117/201,

355/9, 340/173 TP, 346/74 TP, 178/66 TP [51] Int. Cl ..B4lm 5/20 [58] 95/1, 1.7;346/l,74,76, 107,

346/74 P, 74 ES, 74 TP; 41/17, 24, 46, 10, 18; 96/1, 1.1, 1.5; 204/2; 178/66, 7.5, 66 TP; 355/9; 340/173 15] 3,655,371 [4 1 Apr. 11, 1972 2,662,803 12/1953 Schwartz ..346/1 2,418,479 4/1947 Pratt ,41/18 X 2,570,856 10/1951 Pratt ..41/32 2,985,866 5/1961 Norton ..340/173 2,244,304 6/ 1941 Marriage et a1 ..96/67 2,277,013 3/1942 Carlson ..96/1 2,616,961 11/1952 Groak 78/52 2,663,636 12/1953 Middleton ..96/1 2,896,507 7/1959 Mast et a1. ..88/61 3,032,414 5/1962 James ..96/49 3,055,006 9/ 1962 Dreyfoos et al.. ..346/74 3,113,179 12/1963 Glenn ..178/6.6 2,418,479 4/1947 Pratt..... ...41/18 X 2,570,856 10/1951 Pratt ..41/32 2,985,866 5/1961 Norton ..340/173 Primary ExaminerChar1es E. Van Horn Attorney-Marvin A. Goldenberg, Richard V. Lang, Oscar B. Waddell and Frank L. Neuhauser [57] ABSTRACT The disclosure relates to a method and apparatus for storing and reproducing information using a deformable material containing a volumetrically homogeneous distribution of particles for scattering light transmitted through said material. The information can be introduced and read-out in optical form.

14 Claims, 11 Drawing Figures PATENTEMPR 1 3 I972 SHEET 1 BF 5 INVENTOR GEORGE J.CHAFARIS, BY 711mm) MM HIS ATTORNEY.

PATENTEUAPR 1 1 m2 SHEET 2 [1F 5 III!!! ilnlsliw INVENTOR: GEORGE J. CHAFARIS,

HIS ATTORNEY.

PATENTEDAPR 11 I972 SHEET 3 UF 5 INVENTQR GEORGE J. CHAFARIS, B MW HIS ATTORNEY.

NOE

PATENTEDIPRH I972 3,655,371

SHEET I [IF 5 BRIGHT LIGHT F|G.6A l l l l l LIGHT /TRANSPARENT ELECTRODE 3Z$SBIII J PHOTOCONDUCTOR THERMOPLASTIC UNIFORMI-Y CHARGED I x\\\ SCATTERING PARTICLES I FlG 6B B RE$ULTING SURFACE CHARGE Q'QS INDUCED CHARGE SEEM 'IIIIIIIIIIIIII/IIIIIIIIIIIIIIIIIIIIIJI BY SURFACE CHARGE MANY SCATTERING PARTICLES PASS LIGHT F IG.6C THROXGH PROJECTION SYSTEM THERMOPLASTIC LAYER /RESULTING SURFACE w, B DEFORMATIQN AF ER DEIIEL MENT (FEW SCATTERWG PARTICLES) PERCENT SHUTTER OPENING I00% I FIGS A I I I l l I I CHARGE CIRCUIT CLOSED I I DISCHARGE CIRCUIT I I I I I CLOSE I 'JIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIII I I I I I SOLENOID CIRCUIT CLOSED D k\\\\\\ \\\\\\\W I I I I L I I I E T In In+I Tn+5 In+6 CbI an n Rpl FIG'4 INVENTORZ HIS ATTOR N EY.

PATENTEDAPR 1 1 I972 SHEET 5 OF 5 INVENTOR GEORGE J. CHAFARIS,

HIS ATTORNEY.

METHOD AND APPARATUS FOR REPRODUCING OPTICAL INFORMATION The present invention relates to a method of and apparatus for reproducing information, and to a novel medium for storing said information, and relates more particularly to a reproducing system wherein information is introduced and read-out in optical form, said information being stored by a physically deformable member.

Both military an commercial requirements for a long time have existed for recording a replica of a phenomenon in such a manner that it can be faithfully analyzed at a later time. The requirements for recording duration, bandwidth, and number of channels have become more demanding with the passage of time. Among the techniques that have been used in satisfying these requirements are those of photographic recording, magnetic tape recording, dielectric recording, which is accomplished by placing a charge distribution on the surface of a dielectric or by inducing a polarization in the volume of a dielectric, and others. More recently thermoplastic recording has been attempted and has been shown to have certain advantages over other recording methods. A complete disclosure of such a system may be found in an application for US. Letters Patent Ser. No. 698,167 titled Method and Apparatus for Electronic Recording" filed Nov. 22, 1957 by William Glenn and assigned to the present assignee now abandoned.

The above referred to reproducing systems lack the ability to reproduce optical information in a simple and expedient manner. The instant invention is intended to satisfy this need and provides a system that is able to directly receive information in optical form, similar to photographic recording, but which information is processed, stored and readied for display within a fraction of a second. The processing or developing operation is performed by an electrical process. The system additionally utilizes a reusable storage medium.

The earlier method of thermoplastic recording proposed by Glenn, which present invention invention seeks to improve, utilizes as the storage medium a deformable, clear thermoplastic tape. Generally, this earlier method is an improvement over a known technique of writing information on an oil film by the application of electrical charges from a scanning modulated electron beam. In this technique, the oil film is deformed to contain optical line gratings of variable depth by the action of the electrostatic forces of adjacent electrical surface charges deposited by the beam, but the gratings are retained only so long as the electrical charges are present. When these charges leak off, the oil film resumes its normally even contour. A suitable optical system, similar to that presently to be described with relation to FIG. 7, is utilized in reading out the information from the deformed oil film. In this manner theatre size projection of television signals has been accomplished.

The use of thermoplastic tape in lieu of the oil film, as in the above mentioned system, has the advantage of obtaining a permanent record or recording of the input information. The thermoplastic tape is effectively a very high resolution, reusable photographic-like film that is developed almost instantaneously by non-chemical means. In the Glenn method as in the oil film technique, information to be stored is amplitude or velocity modulated on a scanning electron beam. in explaining the operation of this system, we will consider only amplitude modulation which is commonly used for the recording of black and white television pictures. The information is deposited on the surface of the thermoplastic tape in the form of a geometrical distribution of electrical charges. As a result of the surface scanning, which for television pictures is at the conventional rate of 525 lines per frame, these charges are laid down as a raster having many lines of charges. Each elemental portion of each scanned line develops a particular charge value corresponding to the beam intensity at that element. By application of heat to the thermoplastic material which softens the material, the lines of charges deform into optical gratings, as will be explained below, which are in the gratings are relatively deep,

- wherein the instantaneous shape of ripples. This due to the action of the electrostatic forces of the line charges. Upon cooling, the deformations become set and each bit of information or picture element is stored in the thermoplastic tape as an elemental optical grating. The optical gratings are formed by the beam along parallel lines in the direction of scanning. They consist of troughs and crests, wherein the troughs are formed by the lines of charges deposited by the electron beam causing rut-like depressions in the surface of the tape and the crests" by the spacings between scanned lines, the elevation of which is substantially unaffected. A ripple effect is thereby created depth of the ripple troughs is approximately proportional to the charge density as determined by the amplitude of the signal applied to the electron beam. For high intensity or bright signals the troughs are made deeper, and for low intensity signals they are less deep. In this manner the input information is stored in the surface deformations of the thermoplastic medium, more specifically being stored in the optical grating lines formed on said surface, from which the information may be recovered as a result of the dif fractive (or refractive) properties of said gratings.

A special type of projection system, which is a form of optical phase demodulation system, is utilized for recovering the information stored in the diffraction (or refraction) gratings. Briefly, the system responds to diffracted (or refracted) light which is transmitted to a screen or other read-out medium, through the modulated thermoplastic medium. As opposed to conventional slide projection systems, this type of a system is non-responsive to density variations. The diffraction (or refraction) of the light occurs when light is incident upon the slope portions of the gratings, and the extent thereof is a function of the slope. Diffraction and refraction may be distinguished in that refraction effects contemplate large incident surfaces relative to the wavelength of light, and are explained by the simple rules of geometrical optics. Diffraction effects contemplate small incident surfaces relative to the light wavelength, and require explanation by Huygens optical principles. Thus whether the projected light is considered to be refracted or diffracted depends upon the dimensioning of the gratings as related to the wavelength of light. Both of these properties are referred to in accounting for the dispersive phenomenon of the light contributed by the gratings. With a modulated tape placed in this type of projection system, the portions of the image formed on the tape, wherein the rippled corresponding to bright picture areas, will disperse a considerable amount of light. Hence the light output transmitted to the screen, being determined by the amount of dispersion, will also be considerable. The portions corresponding to darkness, wherein the gratings are shallow, will disperse and hence cause transmission of little light to the screen. The information on the tape is thus recovered and may be utilized directly by displaying on a screen, as indicated above, or may be converted to an electrical signal by a photoelectric device for further processing.

When the information to be handled in such prior art thermoplastic reproducing systems as described above is of an optical nature, such as a picture image, it is seen that it is necessary to first scan the picture to convert the light energy to electrical energy which is then used to modulate an electron beam. The writing operation is thus required to be performed within a vacuum which necessitates enclosing at least the tape and tape reels in a vacuum chamber and providing effective vacuum seals and pumps. The present invention avoids the necessity of obtaining a scanned intermediate electrical signal by introducing the light information to the thermoplastic tape directly as an optical signal rather than as an electrical signal. This direct introduction of the light information is accomplished by use of a two dimensioned charged surface representative of the optical image.

It should be understood at this point that use of the grating technique, above referred to, wherein the diffractive (or refractive) properties of the slope portions of the grating are utilized during read-out, is not possible when introducing light information directly to the thermoplastic storage medium. This is so because light thus introduced produces no grating lines on the thermoplastic material. Rather surface deformations are formed on the thermoplastic at each elemental area in accordance with the intensity of the light input. The slope portions formed by these surface deformations cannot be used in an optical projector to give an accurate read-out. For example, both, extensive bright portions and dark portions of a picture would appear similarly as a dark output, since the surface contour for these portions would be flat and have a zero slope. Only the boundaries between right and dark portions would have a slope and appear bright.

Optical information has been introduced directly in recording systems of the prior art, but these systems are of limited or distinctly different application. In one such system, using a xerographic process which employs a photoconducting plate, electrical charges are formed on the surface of a uniformly charged selenium plate by the selective discharging action of an applied optical image. This process has been used in printing, etching, or electroplating processes but has found no known application to optical projection systems.

In another system an ultraviolet light when applied to an ultraviolet-sensitive plastic emulsion, will release small quantities of nitrogen gas which is held under pressure by the plastic emulsion. Upon heating, the plastic is temporarily softened allowing the gas to expand, forming tiny bubbles. Such system is used for the production of projection positives from black and white negatives or for the production of black and white negatives from color transparencies. The negatives are placed in a printer wherein a source of ultraviolet light is transmitted through the negatives to the sensitive plastic. In development, bubbles are formed in the plastic in accordance with the intensity of the impinging ultraviolet light. The color transparencies are similarly printed. Projection is performed in a conventional projector, the bubbles scattering the transmitted light rays and having the same effect as the opaque silver image in conventional films. This system, although advantageous in producing positive and negative transparencies without the need for chemicals and under normal room-lighting conditions, cannot be used for taking pictures at hand held shutter speeds because of the requirement of ultraviolet light. Further, the special plastic is not subject to reuse.

It should be recognized that distinct limitations exist in prior art recording techniques in the handling of optical information. In most systems it has been necessary in the past to convert the optical information to electrical energy which must be applied to cumbersome electronic apparatus in the writing operation. In devices where optical energy has been introduced directly, there has been limited application. The instant invention is intended to overcome these limitations and to be an improvement over the prior art systems. Optical information in the form of ordinary light may be introduced directly to a simple, portable recording equipment. The recordings obtained are of a high resolution. No vacuum is necessary in the writing operation. The recording medium may be used recurrently. The recording and developing operations are substantially instantaneous, requiring as little as a fraction of a second. The recorded information is susceptible to being read-out by optical means and may be projected on a screen or converted into electrical energy for further processing by being applied to a photoconductive device. The instant invention is flexible in its application. It may be used to record purely optical images, such as in conventional photography, or it may record electrical information which has been converted into light energy, such as information on a radar screen or a flying spot scanner. Moreover, the rate of recording is sufficiently rapid for recording motion as well as still subject matter.

It is accordingly a primary object of the present invention to provide a novel method for the storage, processing and display of information which is introduced optically.

It is a further object of the invention to provide a novel reproducing apparatus for the storage, processing, and display of information which is introduced optically.

A further object of the invention is the provision of a transparent thermoplastic tape of novel composition for use in a reproducing system wherein read-out is achieved in a suitable optical projection system.

Another object of the invention is to provide a novel system for the recording and displaying of an optical image by recording said image upon a thermoplastic medium and displaying said image by use of a suitable optical projection system which responds to scattered light.

A further object of the invention is to provide an optical image reproducing system in which information is applied by electrical means upon a reusable storage medium without the requirement of a vacuum.

Still a further object of the present invention is the provision of a reproducing system in which read-out of a thermoplastic tape is accomplished by means of a suitable projector responsive to scattered light, wherein the novel composition of the thermoplastic tape provides a scattering of the projected light.

These and other objects of the invention are achieved in a novel reproducing system useful for the storage, processing, and display of information which is introduced as an optical image, or other optical form, to a recording apparatus. A novel storage medium is utilized which comprises a transparent thermoplastic tape having embedded therein a homogeneous distribution of tiny light scattering particles, In recording an optical image each elemental area of the surface of a selected portion of the thermoplastic tape is variably charged to form an electrostatic image which is in conformance with the received optical image, by means of a contiguous photoconductive material. The tape is then transformed to a fluid state by heating and is then deformed by the action of the electrostatic forces of the surface charges, resulting in a thickness modulation of said tape. Read-out is accomplished by placing the modulated tape in a suitable optical system responsive to scattered light, one similar to the type used in the earlier thermoplastic recording, in which the extent of the scattering of projected light by the tape determines the information obtained.

The recorded information in the present invention is contained in the instantaneous thickness of elemental areas of the thermoplastic material in which the particles are uniformly distributed. The thickness of this material at any point is made to vary in accordance with the light intensity of the applied image. The thicker elemental portions thus contain a larger number of scattering particles and create a brighter area in the output image when displayed in the optical projectonThe light intensity of each elemental area of an image as it appears on the projection screen is determined by and is a function of the number of scattering particles contained at the corresponding elemental area of the modulated tape. Thus the projected light is intensity modulated by the scattering particles to form the desired image. This read-out is seen to significantly differ from the earlier method of thermoplastic recording using a grating technique with a clear thermoplastic material, wherein the information is contained in surface ripples and the projected light in the optical system is diffracted or refracted by the variable slope surface portions of the ripples.

The invention will be better understood from the following description taken in connection with the accompanying drawings and its scope will be pointed out in the appended claims.

In the drawings,

FIG. 1 is an isometric view of applicants overall reproducing system;

FIG. 2 is an isometric view of an alternative embodiment of applicants reproducing system;

FIG. 3 is a diagram of a composite recording and developing apparatus used in the novel system illustrated in FIG. 1;

FIG. 3a is a cross sectional view of the thermoplastic tape magnified many times actual size;

FIG. 3b is an illustration of a portion of FIG. 3 in an operational sequence wherein the tape is out of contact with the pressure plate and the photoconductive device;

FIG. 4 is a schematic diagram of the charge-discharge circuits of FIG. 3;

FIG. 5 is a timing chart illustrating the timing relationship between the shutter operation and the synchronized switching circuitry;

FIGS. 6A, 6B, and 6C are diagrams illustrating the physical principles involved in obtaining thickness modulation of the thermoplastic material; and

FIG. 7 is an explanatory diagram of a suitable projection system which may be used in the present invention.

Referring to FIG. 1 there is shown an isometric view of an embodiment of applicants thermoplastic tape reproducing system consisting of a recording or encoding device 1 and a projection system 2. Encoder 1, shown in detail in FIG. 3, takes the general form of a camera and is adapted to receive optical information in the form of an image I. The encoder is shown to comprise a lens barrel 3, a shutter release button 4 and a shutter reset lever 5. The encoder performs the function of thickness-modulating the tape 29 in accordance with the received optical image, the tape being handled within the apparatus by a tape transport mechanism, comprising a feed reel 37 and a take-up reel 38, guide sprockets 35 and 36, and a mechanical drive, not shown. Read-out of the modulated tape is accomplished by a projector 8, whose lens system is illustrated in FIG. 7, wherein a facsimile of the received image is projected on screen 9. The projector includes a projection lamp 19, a tape transport mechanism for handling rolls of modulated thermoplastic tape 29', comprising a feed reel 10 and take-up reel 11, and guide sprockets l7 and 18, shown in position with the lens system. The lens system includes lenses 60, 62 and 64 and bar systems 61 and 63 having concentric annular opaque and transparent portions.

The illustrated system, comprising elements 1 and 8, is for the taking and projecting of still pictures, or slides. It should be understood, however, that the present invention is not limited to processing stills since the rate of taking pictures may be set at many times the rate necessary for motion picture projection, the actual exposure and development time being within a fraction of a second.

If desired, the projector and recorder units may be combined in a single structure, such as unit 14 shown in FIG. 2, wherein the tape transport mechanism comprising feed reel 15 and take-up reel 16 carries the developed tape directly to the projector. In this manner the three sequences of operation, expose, develop, and display, may be performed in uninterrupted fashion. The component structural parts and the circuitry included in unit 14 are essentially the same as contained in encoder 2 and projector 8.

Referring to the detailed illustration of the encoder in FIG. 3, an optical image I is impressed on to a transparent thermoplastic tape 29 in the form of distributed electrical charges. In the illustration shown, which is merely a schematic representation, received light passes through an optical lens 21 which focuses the image through an adjustable diaphragm 22, which controls the exposure, through shutter 23 upon a layer of photoconductive material 28. Button 4 operates the shutter and lever 5 performs the reset. The lens, diaphragm, and shutter are standard photographic components which may be found in a conventional still or motion picture camera. 35MM camera parts are applicable but other size camera components can be used. A suitable form of shutter is the Kodak Flash Supermatic shutter manufactured by the Eastman Kodak Company of Rochester, New York. A photoconductive device 24 is provided which comprises a non-conducting mounting frame 25, a thin optically flat glass plate 26, on which is deposited, in a known manner, a thin layer of tin oxide 27 or a similar transparent electrically conducting layer. The photoconductive material 28 abuts the conducting layer so that good electrical contact is made. The photoconductive material may be cadmium sulfide, or a similar material possessing photoconductive properties, and although shown relatively thick with respect to the conducting layer may have thickness dimensions comparable to said layer.

The thermoplastic tape 29, upon which an electrostatic image charge is applied by means of the photoconductive material, is preferably of three layer construction. This construction is seen more clearly in FIG. 3a. The base layer 33 is a motion picture film stock of l-3 mils thickness capable of withstanding the heat of development, l00 to 150 C. Lexan, a product of the General Electric Company, Mylar or Cronar, both products of the E. I. DuPont de Nemours & Company, are suitable. The intermediate layer 32 is preferably of evaporated chromium which is a transparent highly conductive material, usually deposited to about 1 micron in thickness. Other material such as a cuprous iodide may be used. The third layer is a transparent thermoplastic material 31 in which are embedded a homogeneous distribution of tiny light scat tering particles 30, l to 5 microns in diameter. A polystyrene preferably PS-2 hyperclean polystyrene, the number indicating the molecular weight, in the order of 20 microns to l mil thickness, is suitable for the material 31. The melting point of the polystyrene is in the range of to l50 C. This is appreciably lower than the melting point of the plastic film stock. The scattering particles 30 may be transparent, in the form of air entrapped glass bubbles or finely ground glass particles, whose index of refraction is different from that of the thermoplastic material. Or they may be opaque, such as carbon black. They are embedded by being mixed in a liquified form of thermoplastic material, in a density to effectively scatter light transmitted through the tape without substantial attenuation of the light as it emerges from the tape.

The thermoplastic tape transport and positioning mechanism of FIG. 3 transports the tape in position for exposure in the encoder, during exposure holds the thermoplastic layer in contact with the photoconductive device, and after exposure transports the tape through the developing position. This mechanism comprises a feed reel 37 and take-up reel 38, driven either manually, or by a drive motor 44, as shown. Sprockets 35 and 36 and idler wheels 52 and 53 serve to guide the tape into a position adjacent the photoconductive device, but separated therefrom. The sprockets are set back and exert a tension to maintain the tape displaced from the photoconductive device when the tape is not being forced against the photoconductor, as during its longitudinal movement. This displaced position is shown in FIG. 3b. In the proper operational sequence, as will be presently understood, metal pressure plate 34 forces the tape against the photoconductor so that good electrical contact is made between the thermoplastic material 31 and the photoconductive material 28 and between the pressure plate 34 and the Mylar base 33. The solenoid actuated rod 41 working against tension springs 42 and 43 actuate the pressure plate 34 in a transverse direction into and out of contact with material 31. The solenoid is energized by a circuit through switch S2.

With plate 34 in contact with base 33 a charge circuit for the thermoplastic tape is formed by the plate 34 being electrically connected at its lower end through conductor 45 to a single pole triple throw switch S1. Switch S1, as well as switch S2, are mechanically linked to the shutter mechanism and shutter reset mechanism contained in a housing 20 by means of shaft 50 coupled to the shaft, not shown, which supports the shutter reset lever 5. Operation of the shutter serves to synchronously move the switches in the direction shown, as the shutter reset lever 5 moves. Movement of the shutter reset lever 5 to reset the shutter mechanism additionally serves to reset the switches S1 and S2 to position 1. Contact l of switch S1 is connected to the positive terminal of battery Bl having voltage in the range of 300 to 1,000 volts. When the recorder is not in use, S1 will normally be in this charge position. It is seen that a closed circuit, including conductor 46 and conducting layer 27, thereby connects the battery in series with the thermoplastic tape 29 and the photoconductive material 28 so that a charge of the total battery voltage is placed across the thermoplastic tape 29. Contact 2 of switch S1 is commonly connected to the negative terminal of battery B1 and to the conducting layer 27 of the photoconductive device. When S1 is connected to contact 2, which is the expose or discharge position, a discharge path is formed for the charge previously developed across the thermoplastic tape, from the surface of the thermoplastic material 31 through the photoconductive material 28 to the transparent conducting layer 27, through conductor 46 to contact 2, through the contact arm of S1 and through conductor 45 to the pressure plate 34. Movement of S1 to position 3 interrupts the discharge circuit.

The discharge path as well as the charge path are illustrated in schematic form in FIG. 4 wherein C,,,-C,,,, are the elemental capacitances across the Mylar base 33, C ,C,,, are the elemental capacitances across the thermoplastic material 31, and R R are the elemental variable resistances of the photoconductive material 28. The components are represented as forming N number of parallel paths. The sum of capacitances C -C is equal to the total capacitance of the base layer 33, which is indicated as C The sum of capacitances C,,C,,, is equal to the total capacitance of the thermoplastic layer 31, and is indicated as C The sum of the resistances R Rpn is equal to the total resistance of the photoconductive layer 28, and is indicated as R In the charge position with switch S1 engaging contact 1, battery Bl will charge the base capacitance C and the thermoplastic material capacitance C through the photoconductor resistance R which is in its high resistance state. After a finite period the total battery voltage is distributed across capacitors C and C The component values of the circuit are selected So that approximately half of the voltage appears across C This provides for retaining a sufficient amount of charge across C, after the discharge operation to readily deform the thermoplastic material when heated to l00150 C. A variable discharge of C occurs when S1 is moved to contact 2, R having been exposed to light, now being in a low resistance state with the resistance in each path different as determined by the light intensity at each point of the photoconductive material. Movement of S1 to contact 3, which is unconnected, opens the discharge circuit, and provides for retaining a variable charge on the capacitance C The value of gamma may be controlled by interrupting the discharge operation, the latter being related to the exposure time and diaphragm setting, within a time determined by the RC time constant of the circuit in elements of bright exposure. If, for example, parallel branch 1 represents and element of bright exposure, its RC time constant is low as compared to a branch of dark exposure, and the duration of the discharge operation is within said low time constant. As a result, the variable charge that is retained on the surface of the thermoplastic tape is in conformance with the received optical image. The above method of charging and discharging the thermoplastic tape using a photoconductive device is the preferred form. However, it should be understood that alternative methods may be used such as charging xerographic plate in accordance with a light image and transferring the charge to the thermoplastic tape by joining the charged surface of the xerographic plate and the thermoplastic layer and connecting the tape conducting layer to the backing electrode of the xerographic plate. Another method is to maintain the thermoplastic capacitance C in a normally discharged condition, and upon exposure, to variably charge the elemental capacitances C,,C,,,. Gamma is then determined by the time constant of the charge circuit.

Referring again to FIG. 3, the tape is developed when the switch S1 is in position 3. For this purpose a radiant heater circuit is provided including battery B3 whose positive terminal is connected through switch S3 to one side of heater element 47, which may, for example, be a Nichrome wire, and the negative terminal is connected to the other side of element 47. A coil form 48 supports the heater element. The battery B3 provides a voltage sufficient to raise the temperature of the thermoplastic material to l00l50 C. In this temperature range the physical property of the selectably softenable thermoplastic material is changed from a solid to a fluid or softened state whereas the film stock base remains in the solid state. An alternative form of heater apparatus may be used of the induction type. Heat is generated by inducing current in the conducting layer 32, the heat being readily transmitted to the adjoining thermoplastic layer.

In the operation of the illustrated encoder, the shutter release button 4 is mechanically coupled to the shutter operating mechanism and through the shutter reset mechanism to the switches S1 and S2. When button 4 is in the normal position, as shown, the shutter is closed. Switch S1 engages contact 1 and switch S2 engages bar contact 1, the forward edge 7 of which corresponds to contact 1 of S1 which is indicated as position 1, and the rearward edge corresponds to the rearward edge of bar contact 2 of S1. The bar contact of S1 is position 2. S2 in position 1 closes a circuit from battery B2 through S2. conductor 49, to the solenoid 40 back through conductor 51 through switch S4 to the other side of the battery. Solenoid 40 is thereby energized which forces plate 34 in good electrical contact with Mylar base 33, so that a uniform charge is developed across the thermoplastic tape through the photoconductive material 28 which is in its high resistance state. When button 4 is moved inwards to operate the shutter mechanism, shutter 23 opens admitting the optical image or energy. Simultaneously with the opening, S1 engages bar contact 2, and S2 continues to engage its bar contact 1. During the time interval that switch S1 is in position 2 engaging bar contact 2, the length of which is determined by the exposure time, the photoconductive material 28 becomes variably conductive in its elemental sections in accordance with the light intensity applied to it. Accordingly, the charge on the thermoplastic tape will leak off its elemental sections at different rates through a myriad of parallel paths of differing resistance. Simultaneously with the closing of shutter 23, switches S1 and S2 disengage their respective bar contacts, and then travel to position 3 where the contact of S1 is unconnected and the contact of S2 is connected to the drive motor 44. With switch S1 in position 3 the discharge circuit is interrupted which stops the discharge process. The thermoplastic material retains a differential surface charge representing a replica of the light image received. Switch S2 in position 3 opens the circuit to solenoid 40 de-energizing same, and causes the pressure plate to be backed off from the thermoplastic tape by the action of tension springs 42 and 43. Due to the tension exerted on the thermoplastic tape by sprockets 35 and 36, the tape will accordingly take a position clear of the photoconductive device and the pressure plate. The position of the tape with respect to the pressure plate and the photoconductive device in this sequence of operation is shown clearly in FIG. 3b. Switch S2 in position 3 also closes a circuit to single frame drive motor 44 which drives the tape through one frame to a position adjacent heater element 47.

With the tape adjacent the heater in the development position, the closing of switch S3 energizes the heater element which heats and thereby liquefies the exposed portion of the thermoplastic material causing it to deform by the action of the electrostatic forces applied by the surface charges. This results in a thickness modulation of the material wherein the number of particles in elemental portions of the thermoplastic material is proportional to the thickness of the material. Release of switch S3 opens the heater circuit and allows the tape to cool in its deformed shape, retaining the originally received light information in the form of a thickness modulation. In the cooling process, the Mylar base acts as a heat sink. The reset mechanism actuated by reset lever 5, which is mechanically coupled to the shutter and to switches S1 and S2, as previously mentioned, simultaneously acts to cock the shutter and to reset the switches S1 and S2 to position 1. The encoder is thus ready for the succeeding optical information. It is noted that with switch S4 in the open position, a double exposure may be obtained. This opens the circuit to the frame drive mechanism and prevents the tape from being moved to the develop position adjacent to the heater after a exposure sequence. When a modulated tape is to be used again, in normal operation it need only be put through the recording operation described above, wherein erase and re-write can be carried out simultaneously. If the tape is to be reused within 30 seconds to one minute, electrical charges may remain trapped within the thermoplastic material and it is desirable to erase the tape by reheating before re-writing.

The timing sequence of the operation of switches S1 and S2 and the shutter as they related to the above described operation can be readily understood by referring to FIG. 5. Graph A shows the shutter operation with respect to time. Graph B shows the charge circuit operation with respect to time. Graph C shows the discharge circuit operation with respect to time. Graph D shows the solenoid energizing circuit operation with respect to time, and graph E shows the drive mechanism energizing circuit operation with respect to time. It is seen that the charge circuit, with switch S1 engaging contact 1, is closed for a time of n intervals during which time the thermoplastic tape receives its even charge. This is the normal position of S1. During this time the solenoid energizing circuit is also closed maintaining the pressure plate in its position in contact with the thermoplastic tape. At time tn, the shutter operation commences and the charge circuit opens as S1 breaks engagement with contact 1. The shutter reaches the maximum open position at time MI I, at which time the discharge circuit closes by S1 engaging bar contact 2. As shown, at predetermined time m/S, which time is determined by the exposure setting, the shutter begins to close. A this point the discharge circuit and the solenoid energizing circuit open, as switches S1 and S2 respectively disengage their bar contacts 1 and 2. At time tn/6 the drive mechanism energization circuit is energized to move the tape a distance of one frame. This circuit remains energized until the switches S1 and S2 are reset to position 1 by shutter reset lever 5. The timing sequences indicated are exemplary and may be modified in several respects without exceeding the scope of the invention. For example, the charge circuit need not be opened at the moment of the shutter operation but may be opened earlier, and the drive energizing circuit need not be closed at the moment that the shutter closes. It is advantageous that the discharge circuit be closed during the time that the shutter is open for optical efficiency.

It should be understood that the mechanical operation of the switches, shutter and transport mechanism described herein is merely exemplary and is not intendedto form a part of this invention. For example, if desired, the reset mechanism may be automatic, operating at a finite time after the shutter is actuated, or the develop switch S4 may be automatically actuated. In a further alternative arrangement, the entire sequence of operation may be made automatic so that a succession of pictures are encoded and developed by operating a single lever, similar to a motion picture camera.

FIGS. 6A, 6B, 6C illustrate the manner in which the electrical charges, having been formed on the tape surface by the impinging light, serve to deform the thermoplastic material. During the expose operational sequence, shown in FIG. 6A, bright light is applied to portion A of the photoconductor and absence of light to adjacent portion B. This allows charge to run off from the surface of portion A of uniformally charged thermoplastic through the photoconductive material at a much greater rate than from portion B. In a finite time period, corresponding to the exposure time that switch S1 engages bar contact 2, no charge or a minimum charge is retained at portion A while a maximum charge remains on the surface at B, which creates induced charges on the surface opposite, as shown in FIG. 613. During the development sequence, after separation of the thermoplastic tape from the photoconductor, when S1 is in position 3, the thermoplastic material liquifies and the electrostatic forces of repulsion between adjacent surface charges and of attraction between surface and induced charges cause the thermoplastic material to deform, as in FIG. 6C. Portion A is seen to deform negligibly, if at all, whereas portion B deforms appreciably. As illustrated in FIG. 6C, the number of scattering particles per unit surface area in the deformed "portion B is considerably less than in the undeformed portion A. The number is in proportion to the tape thickness since the density of the particles in the material per unit volume remains approximately constant. Another way of describing this is to say that the density of the scattering particles per unit area of the tape surface varies as the tape thickness varies. During projection, light will be scattered to a greater degree by the portion A than by portion B, and bright light will appear on the part of the screen representative of portion A of the tape, whereas that part of the screen representative of portion B will be dark.

The projection operation will be better understood by referring to FIG. 7 of the drawing where read-out of the modulated tape is accomplished using a suitable projection system responsive to scattered light, which is a form of optical demodulation system utilizing phase to amplitude conversion of the modulated projected light energy. A detailed description of a comparable system may be found in U.S. Pat. No. 2,813,146 by Wm. Glenn, issued Nov. 12, 1957. A projection light source at S emits rays of light which are focused by lens 60 and passed through bar system 61, having alternating transparent and opaque portions constructed in annular or rectangular bar form. Light passed by the transparent portions of bar system 61 are focused by lens 62 to normally form an image on corresponding opaque portions of bar system 63. In the absence of any scattering of the light waves traveling between bar systems 61 and 63, no light can reach the projection lens 64, for projection on the screen 65. If the light waves are subjected to scattering they are diverted from their normal path and some of the light will pass around the opaque portions of bar system 63 and be focused on projection screen 65. The amount of light passing through system 63 and appearing on the screen is proportional to the degree of scattering.

The source of light may take the form of a filament which is represented as a line S composed of an infinite number of point sources of light. Considering light from one such point source A, a portion of this light is shown to be in the form of a beam B which is focused by lens 60 to pass through the lower aperture 67 of bar system 61 and through lens 62 which normally forms an image of the aperture 67 on the center opaque portion 68 of bar system 63. By placing the modulated thermoplastic tape to the right of imaging lens 62 (as shown in FIG. 7), the light of beam B is scattered in all directions by an elemental portion 69 of said tape and some will pass around the opaque portions of bar system 63. A typical bundle of scattered light is shown as beam C which is transmitted to the screen and focused on the point X, which corresponds to said tape elemental portion 69. Another portion of the light scattered by the thermoplastic tape from beam B will pass through the lower aperture of bar system 63 to point X on the screen. Each point in the line S may be similarly treated as furnishing a source of light, and as contributing to the final illumination of the point X, the illumination of point X being a function of the area density of scattering particles at the elemental portion 69. Similarly beams are transmitted through each elemental portion of the tape so that the brightness of the corresponding parts of the screen is determined by the degree of scattering of the light transmitted through the tape. Thus by placing the thickness modulated thermoplastic tape 66 between bar systems 61 and 63, the recorded information may be reproduced as a projected optical image. The intensity at any point in the projected image depends on the thickness of the thermoplastic material 31 representing that picture element, since the thickness determines the number of scattering particles in any portion of the thermoplastic material. It is noted that the heating of the thermoplastic tape during read-out is negligible since, unlike density projection of photographic film, the majority of the light impinging on the thermoplastic tape is passed through rather than absorbed.

It is to be understood that the specific embodiment described above is merely illustrative of the general principles of the invention. Various other arrangements can be devised without departing from the spirit and scope of the invention. For example, the intermediate conducting layer may be omitted from the thermoplastic tape and the tape may consist of only the film stock base layer and the thermoplastic layer.

An external backing electrode may be selectively positioned in contact with the base layer during the development operation, much the same as pressure plate 34 is positioned during the charge and discharge operations. The tape may take a further alternative form wherein the conducting layer 32, rather then being the intermediate layer, is an external layer adjoining the film stock base layer. The mechanical linkages including the tape transport mechanism and the synchronized switching circuits may be of other construction. It should also be appreciated that projection systems responsive to scattered light, other than the type illustrated, may be utilized in applicants system without exceeding the scope of the present invention.

While certain embodiments of the invention have been shown and described, it should be understood that the invention is not limited thereto, and it is intended in the appended claims to claim all modifications that fall in the true spirit of the present invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. A medium for storing information in distributed surface elements for use in an optical reproducing system comprising a layer of thermally softenable, transparent, nonconducting material, deformable in thickness, supported by a base layer and a conducting layer, the melting temperature of the deformable material being lower than that of said base and conducting layers, said deformable material having dispersed therein a volumetrically homogeneous distribution of particles for scattering light transmitted through said material, said layer containing a plurality of light scattering particles for each element to cause a light scattering effect as a function of the number of particles in said layer at each said element which number is in turn a function of the thickness of said layer at said element, whereby upon passage of said light through each element of said material after deformation thereof the light is scattered in each element, the extent of the scattering being a function of the thickness of said each element.

2. A storage medium as in claim 1 wherein said particles are of a density to scatter said transmitted light without substantial attenuation thereof.

3. A storage medium as in claim 2 wherein said particles have a diameter in the range of from 1 to 5 microns.

4. A medium for storing information in distributed surface elements for use in an optical reproducing system comprising a transparent tape having a first and second outer layer and an intermediate layer, said first outer layer serving as a supporting layer for the other layers, said intermediate layer consisting of a transparent conductive material, said second outer layer being deformable in thickness and formed of a thermoplastic material having a melting temperature below that of said other layers and having embedded therein a volumetrically homogeneous distribution of light scattering particles for scattering light transmitted through said material, said particles having a diameter in the range of from 1 to 5 microns, said second outer layer containing a plurality of light scattering particles for each element to cause a light scattering effect as a function of the number of particles in said layer at each said element which number is in turn a function of the thickness of said layer at said element, whereby upon passage of transmitted light through each element of said material after deformation thereof said light is scattered in each element, the extent of the scattering being a function of the thickness of said each element.

5. A storage medium as in claim 4 wherein said light scattering particles are of a density to scatter said transmitted light without substantial attenuation thereof.

6. In a reproducing system wherein information is introduced in distributed surface elements in the form of an optical image to a recording device having as the storage medium a reusable transparent tape having a layer of thermoplastic material in which there is embedded a volumetrically homogeneous distribution of light scattering particles, said thermoplastic layer containing a plurality of light scattering particles for each element to cause a light scattering effect as a function of the number of particles in said layer at each said element which number is in turn a function of the thickness of said layer at said element, said optical image being applied to the surface of said transparent tape in the form of a differential charge which is placed thereon by a charge-discharge circuit including a layer of photoconductive material, a method for the storing and processing of said information comprising the steps of: moving a selected portion of said thermoplastic layer and said photoconductive material into electrical contact, uniformly charging each surface element of said selected portion, variably discharging said each surface element by the application of said optical image to said photoconductive layer, there being retained by said surface an electrostatic image which is a replica of said optical image, said electrostatic image exerting electrostatic forces upon said surface, softening said selected portion of said layer of thermoplastic material by applying heat thereto whereby said electrostatic forces produce a thickness modulation of said portion, said thickness modulation causing the number of light scattering particles for said surface elements of said selected portion to be varied.

7. In a reproducing system wherein information is introduced in distributed surface elements in the form of an optical image to a recording device having as the storage medium a reusable transparent thermoplastic tape having a layer of thermoplastic material in which is embedded a volumetrically homogeneous distribution of light scattering particles, said thermoplastic layer containing a plurality of light scattering particles for each element to cause a light scattering effect as a function of the number of particles in said layer of each said element which number is in turn a function of the thickness of said element, said optical image being stored in said tape by a charge-discharge circuit which includes a layer of photoconductive material and being read-out from said tape using a suitable projection system, a method for the storing, processing and reading-out of said information comprising the steps of: moving a selected portion of said thermoplastic tape into a first position in electrical contact with said photoconductive material, uniformly charging surface elements in a variable manner through said photoconductive material which material acts as a variable resistance in response to the impinging optical image, there being retained on said surface an electrostatic image which conforms to said optical image, said electrostatic image exerting electrostatic forces upon said surface, moving said selected portion into a second position out of contact with said photoconductive material and adjacent to a heating element, applying a short duration of heat to said selected portion whereby the thermoplastic material of said selected portion is heated to the melting point causing said electrostatic forces to deform said selected portion thereby storing said information as a thickness modulation, the number of said light scattering particles for said surface elements being proportional to the elemental thicknesses, cooling the thermoplastic material of said selected portion, moving said selected portion to a third position within said suitable projection system, and reading-out the stored information by projecting a source of light through said selected portion, whereby the projected light is scattered at said surface elements as a function of said elemental thicknesses, the information being determined by the extent of the scattering.

8. In combination in a recording system adapted to record information introduced in distributed surface elements in the form of an area display, a thermoplastic tape including a layer of transparent non-conducting material having dispersed therein a volumetrically homogeneous distribution of light scattering particles, said layer containing a plurality of light scattering particles for each element to cause a light scattering effect as a function of the number of particles in said layer at each said element which number is in turn a function of the thickness of said layer at said element, a first means for simultaneously charging each surface element of a selected portion of said tape in conformance with said information, and second means for thermally softening said electrically charged selected portion whereby the electrostatic forces exerted by the surface charges produce a variation in the thickness of said portion at said each surface element, said thickness variations containing the recorded information.

9. In combination in a recording system as in claim 8 wherein said first means comprises a layer of photoconductive material.

10. A recording system as in claim 8 wherein said distribution of light scattering particles is of a density to scatter light transmitted through said tape without substantial attenuation of said light.

11. In combination in a reproducing system adapted to store, process and read-out information introduced in distributed surface elements in the form of an optical image, a thermoplastic tape including a layer of thermoplastic material having embedded therein a volumetrically homogeneous distribution of light scattering particles, said thermoplastic layer containing a plurality of light scattering particles for each element to cause a light scattering effect as a function of the number of particles in said layer at each said element which number is in turn a function of the thickness of said layer at said element, photoconductive means for simultaneously charging each surface element of a selected portion of said tape in conformance with the intensity of said optical image, means for thermally softening said electrically charged selected portion whereby the electrostatic forces exerted by the surface charges produce a variation in the thickness at said each surface element resulting in a thickness modulation of said selected portion of said thermoplastic tape, and a phase demodulation projection system responsive to scattered light for reading out said information by projecting a source of light upon the thickness modulated tape, whereby the passage of light through said selected portion of said thickness modulated tape produces a scattering of said light at each surface element, said scattering being a function of the thickness at said each surface element and the read-out information being determined by the extent of the scattering.

12. In combination in a recording system adapted to record information introduced in distributed surface elements in the form of an optical image, a transparent thermoplastic tape having a layer of thermoplastic material in which is embedded a volumetrically homogeneous distribution of light scattering particles, said thermoplastic layer containing a plurality of light scattering particles for each element to cause a light scattering effect as a function of the number of particles in said layer at each said element which number is in turn a function of the thickness of said layer at said element, a layer of photoconductive material, first means for bringing a selected portion of said thermoplastic material and said photoconductive material into electrical contact, a charging circuit for placing a uniform charge on the surface of said selected portion, second means for applying said optical image to said photoconductive material, a discharging circuit including said photoconductive layer for variably discharging said surface in conformance with the intensity of said optical image so as to retain thereon a variable charge in the form of an electrostatic image, said electrostatic image being a replica of said optical image and exerting electrostatic forces upon said surface, and third means for heating said selected portion of the then moplastic material to the softening point whereby said electrostatic forces produce a thickness modulation of said selected portion, said thickness modulation causing the number of light scattering particles for said surface elements of said selected portion of the thermoplastic material to be varied.

13. A recording system as in claim 12 wherein said distribution of light scattering particles is of a density to scatter light transmitted through said tape without substantial attenuation of said light.

14. In combination in a reproducing system adapted to store, process and read-out information introduced in the form of an optical image, a transparent thermoplastic tape having a layer of thermoplastic material in which is embedded a homogeneous distribution of light scattering particles, a layer of photoconductive material, first means for bringing a selected portion of said thermoplastic material and said photoconductive material into electrical contact, a charging circuit for placing a uniform charge on the surface of said selected portion, second means for applying said optical image to said photoconductive material, a discharging circuit including said photoconductive layer for variably discharging said surface in conformance with the intensity of said optical image so as to retain thereon a variable charge in the form of an electrostatic image, said electrostatic image being a replica of said optical image and exerting electrostatic forces upon said surface, third means for heating said selected portion of the thermoplastic material to the softening point whereby said electrostatic forces produce a thickness modulation of said selected portion, said thickness modulation causing the number of light scattering particles for elemental areas of said selected portion of the thermoplastic material to be varied, a projection system comprising a source of light that is projected to a screen through first and second bar systems, each having alternating transparent and opaque portions, said bar systems being placed between said light source and said screen and serving to prevent direct rays of said projected light from reaching said screen, said modulated portion of the thermoplastic tape being placed between said first and second bar systems to receive said projected light and to cause a scattering thereof at said elemental areas which is in direct relation to the number of scattering particles for said areas whereby the scattered light reaching said screen forms thereon a replica of said introduced optical image. 

2. A storage medium as in claim 1 wherein said particles are of a density To scatter said transmitted light without substantial attenuation thereof.
 3. A storage medium as in claim 2 wherein said particles have a diameter in the range of from 1 to 5 microns.
 4. A medium for storing information in distributed surface elements for use in an optical reproducing system comprising a transparent tape having a first and second outer layer and an intermediate layer, said first outer layer serving as a supporting layer for the other layers, said intermediate layer consisting of a transparent conductive material, said second outer layer being deformable in thickness and formed of a thermoplastic material having a melting temperature below that of said other layers and having embedded therein a volumetrically homogeneous distribution of light scattering particles for scattering light transmitted through said material, said particles having a diameter in the range of from 1 to 5 microns, said second outer layer containing a plurality of light scattering particles for each element to cause a light scattering effect as a function of the number of particles in said layer at each said element which number is in turn a function of the thickness of said layer at said element, whereby upon passage of transmitted light through each element of said material after deformation thereof said light is scattered in each element, the extent of the scattering being a function of the thickness of said each element.
 5. A storage medium as in claim 4 wherein said light scattering particles are of a density to scatter said transmitted light without substantial attenuation thereof.
 6. In a reproducing system wherein information is introduced in distributed surface elements in the form of an optical image to a recording device having as the storage medium a reusable transparent tape having a layer of thermoplastic material in which there is embedded a volumetrically homogeneous distribution of light scattering particles, said thermoplastic layer containing a plurality of light scattering particles for each element to cause a light scattering effect as a function of the number of particles in said layer at each said element which number is in turn a function of the thickness of said layer at said element, said optical image being applied to the surface of said transparent tape in the form of a differential charge which is placed thereon by a charge-discharge circuit including a layer of photoconductive material, a method for the storing and processing of said information comprising the steps of: moving a selected portion of said thermoplastic layer and said photoconductive material into electrical contact, uniformly charging each surface element of said selected portion, variably discharging said each surface element by the application of said optical image to said photoconductive layer, there being retained by said surface an electrostatic image which is a replica of said optical image, said electrostatic image exerting electrostatic forces upon said surface, softening said selected portion of said layer of thermoplastic material by applying heat thereto whereby said electrostatic forces produce a thickness modulation of said portion, said thickness modulation causing the number of light scattering particles for said surface elements of said selected portion to be varied.
 7. In a reproducing system wherein information is introduced in distributed surface elements in the form of an optical image to a recording device having as the storage medium a reusable transparent thermoplastic tape having a layer of thermoplastic material in which is embedded a volumetrically homogeneous distribution of light scattering particles, said thermoplastic layer containing a plurality of light scattering particles for each element to cause a light scattering effect as a function of the number of particles in said layer of each said element which number is in turn a function of the thickness of said element, said optical image being stored in said tape by a chargE-discharge circuit which includes a layer of photoconductive material and being read-out from said tape using a suitable projection system, a method for the storing, processing and reading-out of said information comprising the steps of: moving a selected portion of said thermoplastic tape into a first position in electrical contact with said photoconductive material, uniformly charging surface elements in a variable manner through said photoconductive material which material acts as a variable resistance in response to the impinging optical image, there being retained on said surface an electrostatic image which conforms to said optical image, said electrostatic image exerting electrostatic forces upon said surface, moving said selected portion into a second position out of contact with said photoconductive material and adjacent to a heating element, applying a short duration of heat to said selected portion whereby the thermoplastic material of said selected portion is heated to the melting point causing said electrostatic forces to deform said selected portion thereby storing said information as a thickness modulation, the number of said light scattering particles for said surface elements being proportional to the elemental thicknesses, cooling the thermoplastic material of said selected portion, moving said selected portion to a third position within said suitable projection system, and reading-out the stored information by projecting a source of light through said selected portion, whereby the projected light is scattered at said surface elements as a function of said elemental thicknesses, the information being determined by the extent of the scattering.
 8. In combination in a recording system adapted to record information introduced in distributed surface elements in the form of an area display, a thermoplastic tape including a layer of transparent non-conducting material having dispersed therein a volumetrically homogeneous distribution of light scattering particles, said layer containing a plurality of light scattering particles for each element to cause a light scattering effect as a function of the number of particles in said layer at each said element which number is in turn a function of the thickness of said layer at said element, a first means for simultaneously charging each surface element of a selected portion of said tape in conformance with said information, and second means for thermally softening said electrically charged selected portion whereby the electrostatic forces exerted by the surface charges produce a variation in the thickness of said portion at said each surface element, said thickness variations containing the recorded information.
 9. In combination in a recording system as in claim 8 wherein said first means comprises a layer of photoconductive material.
 10. A recording system as in claim 8 wherein said distribution of light scattering particles is of a density to scatter light transmitted through said tape without substantial attenuation of said light.
 11. In combination in a reproducing system adapted to store, process and read-out information introduced in distributed surface elements in the form of an optical image, a thermoplastic tape including a layer of thermoplastic material having embedded therein a volumetrically homogeneous distribution of light scattering particles, said thermoplastic layer containing a plurality of light scattering particles for each element to cause a light scattering effect as a function of the number of particles in said layer at each said element which number is in turn a function of the thickness of said layer at said element, photoconductive means for simultaneously charging each surface element of a selected portion of said tape in conformance with the intensity of said optical image, means for thermally softening said electrically charged selected portion whereby the electrostatic forces exerted by the surface charges produce a variation in the thickness at said each surface elemeNt resulting in a thickness modulation of said selected portion of said thermoplastic tape, and a phase demodulation projection system responsive to scattered light for reading out said information by projecting a source of light upon the thickness modulated tape, whereby the passage of light through said selected portion of said thickness modulated tape produces a scattering of said light at each surface element, said scattering being a function of the thickness at said each surface element and the read-out information being determined by the extent of the scattering.
 12. In combination in a recording system adapted to record information introduced in distributed surface elements in the form of an optical image, a transparent thermoplastic tape having a layer of thermoplastic material in which is embedded a volumetrically homogeneous distribution of light scattering particles, said thermoplastic layer containing a plurality of light scattering particles for each element to cause a light scattering effect as a function of the number of particles in said layer at each said element which number is in turn a function of the thickness of said layer at said element, a layer of photoconductive material, first means for bringing a selected portion of said thermoplastic material and said photoconductive material into electrical contact, a charging circuit for placing a uniform charge on the surface of said selected portion, second means for applying said optical image to said photoconductive material, a discharging circuit including said photoconductive layer for variably discharging said surface in conformance with the intensity of said optical image so as to retain thereon a variable charge in the form of an electrostatic image, said electrostatic image being a replica of said optical image and exerting electrostatic forces upon said surface, and third means for heating said selected portion of the thermoplastic material to the softening point whereby said electrostatic forces produce a thickness modulation of said selected portion, said thickness modulation causing the number of light scattering particles for said surface elements of said selected portion of the thermoplastic material to be varied.
 13. A recording system as in claim 12 wherein said distribution of light scattering particles is of a density to scatter light transmitted through said tape without substantial attenuation of said light.
 14. In combination in a reproducing system adapted to store, process and read-out information introduced in the form of an optical image, a transparent thermoplastic tape having a layer of thermoplastic material in which is embedded a homogeneous distribution of light scattering particles, a layer of photoconductive material, first means for bringing a selected portion of said thermoplastic material and said photoconductive material into electrical contact, a charging circuit for placing a uniform charge on the surface of said selected portion, second means for applying said optical image to said photoconductive material, a discharging circuit including said photoconductive layer for variably discharging said surface in conformance with the intensity of said optical image so as to retain thereon a variable charge in the form of an electrostatic image, said electrostatic image being a replica of said optical image and exerting electrostatic forces upon said surface, third means for heating said selected portion of the thermoplastic material to the softening point whereby said electrostatic forces produce a thickness modulation of said selected portion, said thickness modulation causing the number of light scattering particles for elemental areas of said selected portion of the thermoplastic material to be varied, a projection system comprising a source of light that is projected to a screen through first and second bar systems, each having alternating transparent and opaque portions, said bar systems being placed between said light source and said screen and serving to prevent direct Rays of said projected light from reaching said screen, said modulated portion of the thermoplastic tape being placed between said first and second bar systems to receive said projected light and to cause a scattering thereof at said elemental areas which is in direct relation to the number of scattering particles for said areas whereby the scattered light reaching said screen forms thereon a replica of said introduced optical image. 